1. Field of the Invention
The present invention relates to an optical control apparatus, an optical junction apparatus and an optical ADM apparatus and an optical transmission apparatus having the apparatus.
2. Description of Related Art
High reliability is requested in an optical submarine system. In such a system, a detour path is prepared as an auxiliary optical transmission system route in preparation for a case in which trouble is caused in a certain repeater or a cable. There is needed an optical junction apparatus for switching to transmission by the detour path when trouble is caused.
In the meantime, according to the optical junction apparatus in the above-described system, path switching must frequently be operated remotely when trouble is caused after a trouble spot has been specified by a test signal from an end office apparatus or the like. Therefore, the optical junction apparatus is requested to be able to operate to switch by a control signal from a remote location. As an optical junction apparatus capable of carrying out such a switching operation, there has conventionally known a constitution incorporating an optical switch for switching an optical path by mechanically moving an optical part such as a prism or the like by receiving a control signal from outside.
On the other hand, in order to deal with large capacity formation of a transmission capacity in recent years and to construct a flexible network among a plurality of stations, there has been reduced to practice wavelength division multiplexing optical transmission (hereinafter, referred to as xe2x80x9cWDM optical transmissionxe2x80x9d) using optical ADM apparatus. According to the WDM optical transmission using optical ADM (add-drop multiplexer) apparatus, optical ADM apparatus are arranged at transit stations arranged among end offices. End offices and transit stations are connected by optical transmission paths and there is transmitted wavelength division multiplexing light (hereinafter, referred to as xe2x80x9cWDM signal lightxe2x80x9d) in which a plurality of signal light having wavelengths different from each other are subjected to wavelength division multiplexing. Signal light having respective wavelength is allocated to respective channel.
The optical ADM apparatus is provided with a function of separating signal light from WDM signal light inputted from an optical transmission path as necessary and inserts the signal light into the optical transmission path when the optical ADM apparatus transmits from a certain transit station to the optical transmission path. There is known a conventional constitution in which in order to separate signal light inputted from an optical transmission path, for example, WDM signal light is temporarily divided into respective wavelengths of signal light by an optical wavelength division demultiplexer. According to the constitution, there is arranged an optical switch for respective divided signal light and by switching the optical switch, there is carried out a selection whether the respective signal light is to be separated to a side of a transit station or transmitted to the optical transmission path as it is.
However, according to the above-described conventional optical division apparatus or optical ADM apparatus, in any of the constitutions, in order to carry out optical path switching or selective sampling of signal light, an optical switch having a movable portion is used and accordingly, there is a certain limit in view of the reliability. Further, according to the optical ADM apparatus, it is also difficult to control separation and insertion of the optical ADM apparatus by a control signal from an end office or the like disposed upstream from the transit station. Levels of signal light which passes through the optical ADM apparatus and is shortcircuited and signal light newly inserted into the optical ADM apparatus need to be the same. However, there also is a case in which depending on the constitution of the optical ADM apparatus, the levels of both significantly differ from each other and the level of the signal light outputted from an optical amplifier needs to adjust.
It is a first object of an optical control apparatus, an optical junction apparatus and an optical ADM apparatus and a WDM optical transmission apparatus using thereof according to the present invention is being capable of controlling optical path switching operation and selective separation and insertion of signal light from outside with high reliability. A second object thereof resides in that adjustment of an output level of signal light outputted from an optical amplifier arranged in an optical ADM apparatus is made unnecessary.
According to an aspect of the present invention, there is provided an optical control apparatus comprising an optical reflector for selectively reflecting only signal light having a specific wavelength in inputted signal light and transmitting signal light having other wavelength and outputting transmitted signal light and a saturable absorber inputted with the transmitted signal light for transmitting the transmitted signal light and outputting first output signal light only when an output level of the transmitted signal light is equal to or larger than a predetermined threshold value. In this case, the optical reflector is inputted further with control signal light in addition to the signal light and when a wavelength of the control signal coincides with the specific wavelength, an output level of the signal light is set to be lower than the threshold value. Conversely, when the wavelength of the control signal does not coincide with the specific wavelength, a sum of the output level of the signal light and an output level of the control signal light is set to exceed the threshold value. The optical reflector can be constituted by using fiber gratings.
The optical junction apparatus according to the present invention is further provided with two optical couplers with the above-described optical control apparatus of the present invention as the basic constitution and carries out division and insertion of signal light by these optical couplers. Specifically, the optical junction apparatus according to the present invention is provided with a first optical coupler for dividing inputted signal light and outputting first divided signal light and second divided signal light, a first optical reflector, a first saturable absorber and a second optical coupler. The first optical reflector is inputted with first divided signal light, reflects selectively only light having a first specific wavelength, transmits light having other wavelength and outputs transmitted signal light. The first saturable absorber is inputted with the transmitted signal light, transmits the transmitted signal light only when an output level of the transmitted signal light is equal to or larger than a predetermined first threshold value and outputs first output signal light. The second optical coupler outputs the first inputted output signal light or second output signal light in the first output signal light and the second output signal light.
According to the above-described constitution, the first optical coupler is further inputted with control signal light in addition to the signal light. When a wavelength of the control signal light coincides with the first specific wavelength, the output level of the signal light inputted to the first saturable absorber is set to be lower than the first threshold value and when the wavelength of the signal light does not coincide with the first specific wavelength, a sum of the output level of the signal light and an output level of the control signal light which are inputted to the first saturable absorber are set to exceed the first threshold value. By adding the control signal light to the signal light, the output of the original signal light can be controlled by controlling the wavelength of the control signal light. Addition of the control signal light to the signal light can be carried out by using light having wavelengths different from each other for the two signal light and wavelength division multiplexing the two signal light.
When the control signal light is provided with the first specific wavelength, the control signal light is reflected by the optical reflector and accordingly, light inputted to the saturable absorber becomes only the original signal light. At this occasion, the output level of the signal light is set to become lower than the threshold value provided to the saturable absorber and accordingly, the signal light is not outputted from the saturable absorber. In contrast thereto, when the wavelength of the control signal light is shifted from the first specific wavelength, the control signal light is not reflected by the optical reflector and is inputted to the saturable absorber along with the signal light. By two of the signal light at this occasion, the output level is set to exceed the threshold value provided to the saturable absorber and accordingly, the signal light and the control signal light are outputted from the saturable absorber.
Further, according to the optical junction apparatus of the present invention, output control can be carried out by arranging a second optical reflector and a second saturable absorber for other signal light divided by the first optical coupler. In this case, the second optical reflector reflects selectively only second specific light. When the control signal light is provided with the first specific wavelength, the control signal light transmits through the second optical reflector and is reflected when the control signal is provided with the second specific wavelength. In this way, by controlling the wavelength of the control signal light between the first and the second specific wavelengths, an output end of the signal light can be controlled to switch. As the first and the second optical reflectors, for example, fiber gratings can be used.
By providing the second coupler at the poststage of the first saturable absorber, newly inserted signal light can be added.
The optical ADM apparatus according to the present invention is an optical ADM apparatus in which WDM signal light where a plurality of signal light having wavelengths different from each other are subjected to wavelength division multiplexing and control signal light are inputted, only separated signal light having a predetermined wavelength included in the WDM signal light is separated and inserted signal light having the predetermined wavelength is inserted. In this case, the optical ADM apparatus according to the present invention is provided with two of the above-described optical control apparatus. The first optical control apparatus outputs WDM signal light except the separated signal light in the WDM signal light when light having the second specific wavelength is inputted along with the WDM signal light. The second optical control apparatus outputs the WDM signal light as it is when light having the first specific wavelength is inputted. Further, the optical ADM apparatus according to the present invention is provided with a signal optical separating and inserting unit for wavelength division multiplexing the WDM signal light outputted from the optical control apparatus with inserted signal light and outputting wavelength division multiplexed signal light.
The signal light separating and inserting unit can be constituted by a first optical circulator arranged on an input side of the first optical control apparatus, a second optical circulator arranged on an output side of the first optical control apparatus and a signal light reflector arranged between the first optical control apparatus and the second optical circulator for selectively reflecting light having a wavelength of the separated signal light.
A further specific constitution of the optical ADM apparatus according to the present invention is provided with a first optical coupler, a first optical circulator, a first optical reflector, a first saturable absorber, a signal optical reflector, a synthesizing unit, a second optical reflector, a second saturable absorber and a second optical coupler.
The first optical coupler is inputted with WDM signal light in which a plurality of signal light having wavelengths different from each other are subjected to wavelength division multiplexing and outputs first divided WDM signal light and second divided WDM signal light by dividing the WDM signal light. According to the first optical circulator, first divided WDM signal light is inputted from a first port and the first divided WDM signal light is outputted to a second port and the first divided WDM signal light inputted from the second port is outputted to a third port. The first optical reflector is inputted with the first divided WDM signal light and outputs first transmitted WDM signal light by selectively reflecting only light having the first specific wavelength and transmitting light having other wavelength. The first saturable absorber is inputted with the first transmitted WDM signal light and outputs the first output WDM signal light by transmitting the first transmitted WDM signal light when the output level of the first transmitted WDM signal light is equal to or larger than the first threshold value.
The signal light reflector selectively reflects only the separated signal light having the predetermined wavelength from the first output WDM signal light, transmits signal light having other wavelength and outputs transmitted output WDM signal light. The multiplexeing unit wavelength couples the inserted signal light having a wavelength the same as that of the separated signal light and outputs multiplexd signal light to the transmitted output WDM signal light.
The second optical reflector is inputted with the second divided WDM signal light, reflects selectively only light having the second specific wavelength, transmits light having other wavelength and outputs the second transmitted WDM signal light. The second saturable absorber is inputted with the second transmitted WDM signal light and outputs second output WDM signal light by transmitting the second transmitted WDM signal light only when the output level of the second transmitted WDM signal light is equal to or larger than the predetermined second threshold value. The second optical coupler outputs to outside the inputted inserted signal or second output WDM signal light in the inserted signal light and the second output WDM signal light.
The multiplexing unit can be constituted by the second optical circulator in which the transmitted output WDM signal light is inputted from a fourth port, the transmitted output WDM signal light is outputted from a fifth output port and the inserted signal light inputted from the a sixth port is outputted to the fifth port and the inserted signal light inserted with the transmitted output WDM signal and the inserted signal light is outputted. Or, the multiplexing unit can also be constituted by a wavelength division multiplexer for multiplexing light having a wavelength of the signal light included in the transmitted output WDM signal light and light having a wavelength of the inserted signal light.
According to the above-described constitution, the first optical coupler is further inputted with control signal light in addition to the signal light. When the wavelength of the control signal light coincides with the first specific wavelength, the output level of the signal light inputted to the first saturable absorber becomes lower than the first threshold value. Conversely, when the wavelength of the control signal light does not coincide with the first specific wavelength, a sum of the output level of the signal light and the output level of the control signal light inputted to the first saturable absorber is set to exceed the first threshold value.
The first and the second optical reflectors can use fiber gratings similar to the optical junction apparatus. The output side of the second saturable absorber may be arranged with an optical variable attenuator for controlling the output level of the second transmitted WDM signal light.
The optical transmission apparatus according to the present invention is constituted by the above-described optical ADM apparatus and optical end office apparatus for transmitting the WDM signal light in which a plurality of signal light having wavelengths different from each other are subjected to wavelength division multiplexing and the control signal light multiplexed with the WDM signal light. The optical end office apparatus is provided with transmitters for respectively transmitting respective signal light included in the WDM signal light, control signal light sources for transmitting light having first specific wavelength and light having second specific wavelength and a wavelength division multiplexer for multiplexeing the WDM signal light and the control signal light.
The control signal light source is constituted by a first control signal light source for transmitting light having the first specific wavelength, a second control signal light source for transmitting light having the second specific wavelength and an optical switch for switching to output selectively the light having the first specific wavelength and the light having the second specific wavelength. The control signal light source can be constituted also by a light source and a wavelength controller for variably controlling light outputted from the light source to the first specific wavelength or the second specific wavelength.
The optical ADM apparatus is further provided with an optical receiver for receiving the separated signal light and an optical transmitter for transmitting the inserted signal light. In the above-described optical transmission apparatus, an optical amplifier for optically amplifying the WDM signal light and the control signal light may further be arranged between the optical end office apparatus and the optical ADM apparatus.
The optical transmission apparatus according to the present invention is an optical transmission apparatus having a plurality of the optical ADM apparatus according to the present invention, mentioned above, and in which the plurality of ADM apparatus are connected in a ring-like shape via an optical transmission path and the respective optical ADM apparatus is provided with an optical receiver for receiving the separated signal light and an optical transmitter for transmitting the inserted signal light.